Method and structure for eliminating edge peeling in thin-film photovoltaic absorber materials

ABSTRACT

A method for manufacturing a thin-film photovoltaic device includes providing a glass substrate contained sodium species. The glass substrate comprising a surface region and a peripheral edge region surround the surface region. The method further includes forming a barrier material overlying the surface region and partially overlying the peripheral edge region and forming a conductor material overlying the barrier material. Additionally, the method includes forming at least a first trench in a vicinity of the peripheral edge region to remove substantially the conductor material therein and forming precursor materials overlying the patterned conductor material. Furthermore, the method includes thermally treating the precursor materials to transform the precursor materials into a film of photovoltaic absorber. The first trench is configured to maintain the film of photovoltaic absorber substantially free from peeling off the conductor material.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/476,594, filed May 21, 2012, the entire disclosure of which is herebyincorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to techniques for themanufacture of photovoltaic devices. More particularly, the presentinvention provides a method and structure for eliminating peeling of aphotovoltaic absorber film from the lower conductive material. Merely byway of examples, the present method is implemented within a routinepatterning process for the manufacture of thin-film photovoltaic modulesto prevent peeling caused by impurity from edge region of the substrate,but it would be recognized that the invention may have otherapplications.

From the beginning of time, mankind has been challenged to find way ofharnessing energy. Energy comes in the forms such as petrochemical,hydroelectric, nuclear, wind, biomass, solar, and more primitive formssuch as wood and coal. Over the past century, modern civilization hasrelied upon petrochemical energy as an important energy source.Petrochemical energy includes gas and oil. Gas includes lighter formssuch as butane and propane, commonly used to heat homes and serve asfuel for cooking Gas also includes gasoline, diesel, and jet fuel,commonly used for transportation purposes. Heavier forms ofpetrochemicals can also be used to heat homes in some places.Unfortunately, the supply of petrochemical fuel is limited andessentially fixed based upon the amount available on the planet Earth.Additionally, as more people use petroleum products in growing amounts,it is rapidly becoming a scarce resource, which will eventually becomedepleted over time.

More recently, environmentally clean and renewable sources of energyhave been desired. An example of a clean source of energy ishydroelectric power. Hydroelectric power is derived from electricgenerators driven by the flow of water produced by dams such as theHoover Dam in Nevada. The electric power generated is used to power alarge portion of the city of Los Angeles in California. Clean andrenewable sources of energy also include wind, waves, biomass, and thelike. That is, windmills convert wind energy into more useful forms ofenergy such as electricity. Still other types of clean energy includesolar energy. Specific details of solar energy can be found throughoutthe present background and more particularly below.

Solar energy technology generally converts electromagnetic radiationfrom the sun to other useful forms of energy. These other forms ofenergy include thermal energy and electrical power. For electrical powerapplications, solar cells are often used. Although solar energy isenvironmentally clean and has been successful to a point, manylimitations remain to be resolved before it becomes widely usedthroughout the world. As an example, one type of solar cell usescrystalline materials, which are derived from semiconductor materialingots. These crystalline materials can be used to fabricateoptoelectronic devices that include photovoltaic and photodiode devicesthat convert electromagnetic radiation into electrical power. However,crystalline materials are often costly and difficult to make on a largescale. Additionally, devices made from such crystalline materials oftenhave low energy conversion efficiencies. Other types of solar cells use“thin film” technology to form a thin film of photosensitive material tobe used to convert electromagnetic radiation into electrical power.Similar limitations exist with the use of thin film technology in makingsolar cells. That is, efficiencies for thin-film photovoltaic cellsbased on various types of absorber materials are often relatively poor.Recently, many improvements in thin-film material processing have beenachieved in the manufacture of high efficiency monolithic integratedthin-film solar modules on large glass substrates. For example, sodiumdoping is found to enhance the IV characteristics of thecopper-indium-selenium based photovoltaic cells. While un-controlledsodium species in the thin-film photovoltaic cells are also found tocause degradation of the films. In particular, excessive sodium speciesmay cause the thin-film absorber being peeled off from the conductivematerial that serves as bottom electrode, especially from one or moreedge regions. These and other limitations of these conventionalthin-film solar module manufacture techniques can be found throughoutthe present specification and can be improved by applying one or moreembodiments of present invention described in the specification below.

BRIEF SUMMARY OF THE INVENTION

The present invention relates generally to techniques for themanufacture of photovoltaic devices. More particularly, the presentinvention provides a method and structure for eliminating peeling of aphotovoltaic absorber film from the lower conductive material. Merely byway of examples, the method includes patterning a conductive film toform a trench structure to isolate peripheral edge region for ensuringthe thin-film photovoltaic absorber on main surface region substantiallyfree from peeling off caused by impurity from the edge region, but itwould be recognized that the invention may have other applications.

In a specific embodiment, the present invention provides a method formanufacturing a thin-film photovoltaic device free of film peelingproblem. The method includes providing a soda lime glass substratecontaining sodium species and having a surface region and a peripheraledge region surround the surface region. The method further includesforming a barrier material overlying the surface region and partiallyoverlying the peripheral edge region. Additionally, the method includesforming a conductor material overlying the barrier material andpatterning the conductor material to form a plurality of trenches in theconductor material including a first trench formed in vicinities of theperipheral edge region with the conductor material therein substantiallyremoved. Furthermore, the method includes forming two or morethicknesses of precursor materials overlying the patterned conductormaterial. Moreover, the method includes treating the one or morethicknesses of precursor materials at temperatures above 400° C. in anenvironment containing reactive gaseous species to induce atransformation of the one or more thicknesses of precursor materialsinto a film of photovoltaic absorber. The first trench is configured tosurround the surface region for substantially preventing the film ofphotovoltaic absorber on the surface region from peeling off theconductor material.

In another specific embodiment, the invention provides a film structurefor manufacturing a photovoltaic device free of peeling effect. Thestructure includes a glass substrate having a surface region and a bulkregion. The bulk region contains sodium species. The surface region issurrounded by a peripheral edge region. The structure also includes abarrier material overlying the surface region and partially overlyingthe peripheral edge region, and a conductor material overlying thebarrier material and partially overlying the peripheral edge region.Additionally, the structure includes a first trench with thesubstantially all the conductor material therein being removed. Thefirst trench is at least formed a closed loop in a vicinity of theperipheral edge region surrounding the surface region. Further, thestructure includes one or more thicknesses of precursor materialsoverlying the conductor material and at least partially filling thefirst trench. The one or more thicknesses of precursor materials aresubjected to an environment of reactive Selenium gaseous species attemperatures above 400° C. and transformed into a film of photovoltaicabsorber. The film of photovoltaic absorber is characterized bysubstantially free from peeling off the conductor material anywherewithin the surface region surrounded by the first trench.

Many benefits can be achieved by applying the embodiments of the presentinvention. The present invention provides a method for eliminating athin-film peeling-off problem occurred especially in edge regions duringthe manufacture of thin-film solar modules. Certain embodiments of theinvention are implemented for enhancing photovoltaic efficiency byselecting a soda lime glass substrate containing a trace of sodiumspecies. The soda lime glass substrate with rounded peripheral edgeregion is selected based on its overall mechanical strength and otherproperties. Some embodiments are implemented to use a barrier materialfor blocking un-controlled sodium species from diffusing into thin filmsformed for the manufacture of the thin-film solar modules, though asmall portion of sodium species may pass into a conductor (Mo) film atthe rounded edge region where imperfections occur at the transition fromthe glass surface to the ground rounded surface. Such imperfections maylead to poor coverage by the barrier film allowing direct contact ofconductor film to glass in a vicinity of the rounded peripheral edgeregion. Other embodiment includes utilizing one or laser patterningprocesses in a conductor material overlying the barrier material to forma trench in the vicinity around the peripheral edge region to remove theconductor material therein. The trench provides a physical restrictionto the un-wanted sodium species and prevents them entering the conductormaterial along their interface in the major surface region. Thus, duringhigh-temperature treatment of the thin films formed in subsequentprocesses, the possible film peeling-off problem, likely caused byexcessive sodium species, is restricted to the edge region outside thetrench. These and other benefits may be described throughout the presentspecification and more particularly below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method for manufacturing thin-filmphotovoltaic devices free of film peeling according to an embodiment ofthe present invention;

FIGS. 2-11 are simplified diagrams showing a method for manufacturingthin-film photovoltaic devices free of film peeling according to anembodiment of the present invention;

FIG. 12 is a simplified diagram showing a top view of a thin film withstripe patterned structure on a substrate with and a trench formed in avicinity of peripheral edge region according to an embodiment of thepresent invention;

FIG. 13 is a simplified diagram showing a top view of a thin film withstripe patterned structure on a substrate with edge-region film materialdeleted according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to techniques for themanufacture of photovoltaic devices. More particularly, the presentinvention provides a method and structure for eliminating peeling of aphotovoltaic absorber film from the lower conductive material. Merely byway of examples, the present method includes patterning a conductivefilm to form a trench structure to isolate peripheral edge region forensuring the thin-film photovoltaic absorber on main surface regionsubstantially free from peeling off due to impurity from the edge regionof the substrate, but it would be recognized that the invention may haveother applications.

Out of various forms, flat glass panels have been widely used assubstrates for the manufacture of thin-film photovoltaic modules. Arectangular shaped window glass often is a choice for making monolithicthin-film solar module for being installed on a building roof or beingassembled into a solar-energy production system in large-scale fielddeployment. A typical option of the window glass is a soda lime glassmade by float glass techniques. The float glass may be provided as atype with a sharp square edge or another type with an edge rounded by agrinding process. In one or more embodiments, the latter type is foundto be higher in overall mechanical yield with less chance of occurrencein broken parts and edge chips clamshell or loss due to other mechanicalscraps. In one or more additional embodiments, sodium species naturallycontained in the soda lime glass substrate are found to be an importantmaterial ingredient that may positively or negatively affect thethin-film photovoltaic devices formed on the substrate. For example,sodium species as a dopant is found to help causing a larger grain sizeof copper-indium selenide based thin-film photovoltaic absorber thatcontributes an enhanced energy conversion efficiency of the solarmodule. In another example, the sodium species from the soda lime glasssubstrate are also found, if without control, to cause poor deviceperformance and other side-effect quality issues. More details aboutdoping sodium into the thin-film photovoltaic absorber and controllingsodium from the soda lime glass substrate to make advanced thin-filmsolar module can be found in U.S. Patent Application No. 61/523,802,filed on Aug. 15, 2011, commonly assigned to Stion Corporation of SanJose, Calif. and incorporated as a reference for all purposes. Further,embodiments of the present invention, as described throughout thespecification and particularly below, provide techniques formanufacturing thin-film photovoltaic devices substantially without someside-effects caused by the sodium species in the soda lime glasssubstrates.

FIG. 1 is a flowchart illustrating a method for manufacturing thin-filmphotovoltaic devices free of film peeling from edges according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims herein. As shown,the method 100 includes, at least partially, a series of steps orprocesses for forming a thin-film photovoltaic device monolithicallyintegrated on a substrate substantially free of film edge-peelingproblem. In a specific embodiment, the series of steps are summarized asfollowing:

-   1. Start;-   2. Providing a soda lime glass substrate contained a trace of amount    of sodium species;-   3. Forming a barrier material over a surface region of the soda lime    glass substrate;-   4. Forming a conductor material overlying the barrier material;-   5. Patterning the conductor material to form at least a first trench    in a vicinity of a peripheral edge region of the substrate with the    conductor material therein substantially removed;-   6. Forming one or more thicknesses of precursor materials overlying    the patterned conductor material;-   7. Treating the one or more thicknesses of precursor materials at a    temperature above 400° C. to form a film of photovoltaic absorber    surrounded by the first trench substantially free from peeling off    the conductor material;-   8. Stop.

The above sequence of processes provides a method of forming thin-filmphotovoltaic absorber material on a soda lime glass substratesubstantially free from any film peeling problem initiated fromperipheral edge region according to an embodiment of the presentinvention. In a specific embodiment, the method includes advantageouslyutilizing a patterning process to form a first trench into a conductivematerial in a vicinity of a peripheral edge region. The patterningprocess is designated for forming a lower electrode in the conductivematerial configured for a plurality of photovoltaic cells to be formedabove. The conductive material in the first trench is removed to providean extra barrier for preventing excessive amount of sodium species fromdiffusing from the soda lime glass (by passing through a thinned ordiscontinuous barrier material in the peripheral edge region) to aninterface between the thin-film photovoltaic absorber material and theconductive material to cause film peeling off Further details of themethod can be found throughout the present specification and moreparticularly below.

At Step 105, the method 100 starts for the manufacture of a thin-filmsolar device. Step 110 is them introduced to provide a soda lime glasssubstrate containing sodium species. The soda lime glass substrateincludes a surface region and a peripheral edge region surrounded thesurface region. This process is schematically illustrated in FIG. 2. Asshown, an enlarged partial section of a substrate 200 includes a portionof surface region 201 connected to an edge region 202. In a specificembodiment, the soda lime glass substrate is a flat glass panel having arounded peripheral edge region and a rectangular shape with a formfactor of about 65 cm×165 cm or greater. Also shown in this sectionalview, sodium species 203 existed in the soda lime glass. Typically, thesodium species in the soda lime glass exist as an ionic Na⁺ phase inmolecule of sodium oxide (Na₂O). For example, the soda lime glasssubstrate used in this embodiment contains Na⁺ within an ingredient ofabout 14 wt % of Na₂O. In another specific embodiment, the roundedperipheral edge region 202 is gradually curved from the flat surfaceregion 201 toward an end tip. In a much reduced scale, not visible inthis figure, the curved edge region 202 is made of a plurality ofroughened portions including tiny steps or textures. Depending on glassmanufacturer's physical specification, the curvature and local roughnesscan be varied in a certain range. It is noted, the rougher is the edgeregion, the higher is the possibility to cause incomplete coverage of athin film formed overlying thereof. To be seen below, an incompletecoverage of a barrier material film provides a much reduced barrier forsodium species 203 to diffuse through those portions and may induce filmpeeling from the edge region. Embodiments of the present invention justprovide a method to eliminate the cause of the edge peeling problem.

At step 120, a barrier material is formed overlying the soda lime glasssubstrate. As illustrated in FIG. 3, in a specific embodiment, thebarrier material 210 is formed overlying on the surface region 201 witha full coverage as well as overlying the peripheral edge region 202 witha partial coverage. In a specific embodiment, the barrier material 210is selected from silicon dioxide, silicon nitride, silicon oxynitride,or aluminum-containing silicon oxide to serve as a diffusion barrier.The barrier material 210 can be formed using physical deposition,chemical deposition, sputtering, or other techniques. As shown, due tothe curvature and local roughness in the peripheral edge region thedeposited barrier material from above may form a film 212 with smallerand smaller thickness from the portion joined with the flat surfaceregion to the end tip. As mentioned earlier, the soda lime glasscontains certain concentration of Na⁺ ions 203. These sodium species 203can diffuse, especially at elevated temperatures, out of the surfaceregion or the edge region of the glass 200 into a film material overlaidthereof The barrier material 210 (212) is applied over the substrate tosubstantially limit these Na⁺ ions diffusing through, thus establishinga control on the amount of Na⁺ species from the soda lime glasssubstrate to a to-be-formed metallic film. However, the reducedthickness and/or incomplete coverage of the barrier material 212 nearthe peripheral edge region results in an open diffusion path for thesodium species. Because many data show that excessive sodium content incertain metallic films may cause corrosion or other damages to the filmstructure especially a change in shear stress near an interface region.During a thermal treatment with varied and elevated temperatures, filminterface region is likely to lose bonding with a neighboring film,i.e., film peeling can be induced. In our case, the metallic film isessentially one option of a conductor material designated for forming alower electrode of the thin-film photovoltaic device on the substrate.Experiments have been done to prove that, without some edge treatments,the open diffusion path near the edge region may cause leaking of theexcessive sodium ions through the barrier material 212 into theconductive material above to cause edge film peeling off and furtherdiffuse inward to cause larger area film peeling off. Embodiments of thepresent invention just provide a method for eliminating the cause of theedge film peeling off. More details about controlling the soda limespecies directly from soda lime glass into the lower electrode materialand absorber material will be found in later sections of thespecification.

Next process, Process 130, of the method 100 provided in an embodimentof the present invention shown in FIG. 1, includes forming a conductormaterial overlying the barrier material. The conductor material isintended for forming an electrode (lower electric contact) of ato-be-formed thin-film photovoltaic device. This process is visuallyillustrated in FIG. 4. As shown, the conductor material 220 is formed asa film with a fairly uniform thickness overlying the barrier material210. Due to the curvature and roughness of the peripheral edge region202, the deposited conductor material also forms an edge conductive film222 with reduced thickness and/or incomplete coverage. In a specificembodiment, the conductor material 220 or 222 comprises one or morelayers of molybdenum material, for utilizing its good electricalconductivity, strong bonding with copper-indium based photovoltaicabsorber material, as well as its optical properties in visiblespectrum. The one or more layers of molybdenum material can be formedusing one or more deposition processes. For example, the one or morelayers of molybdenum material can be deposited using sputter techniquesunder different sputtering power and chamber pressure in a vacuumchamber.

Referring to FIG. 1, the method 100 further includes a step 140 forpatterning the conductor material to form at least a first trench in avicinity of a peripheral edge region of the substrate with the conductormaterial therein substantially removed. In an embodiment, patterning theconductor material 220 is shown schematically in FIG. 5, as one ofseveral patterning processes for forming lower electrode structure foreach photovoltaic cell. As shown in the sectional view, multipletrenches 230 are formed partially into the conductor material 220overlying the barrier material 210 that extends over the whole surfaceregion 201 (FIG. 3). A specific embodiment of the present inventionutilizes the patterning process for forming a first trench 231 in avicinity of a peripheral edge region. The multiple trenches 230 and thefirst trench 231 can be formed using a mechanical scribing technique orusing laser ablation.

In an embodiment, the laser ablation is used for forming the trenches asa widely-used technique in semiconductor thin-film processing. A laserbeam is applied to illuminate the conductor structure to remove thematerial under the laser spot, forming a line trench by scanning acrossthe surface region. The first trench 231 is a line trench made byilluminating three shifted and overlapped laser spots at onex-coordinate before scanning to next coordinate so that the first trench231 has a wider width than other trenches 230. By controlling laserillumination time and laser power, the conductor material 220 within thefirst trench 231 is substantially removed (in fact, the first trench maybe made deeper by slightly cutting into the barrier material 210). Thefirst trench as formed thus provides a physical restriction band toseparate the surface region that is designated for forming the thin-filmphotovoltaic devices from the surrounding peripheral edge region. In aspecific embodiment, the first trench 231 is formed with about 90 μm inwidth at about 4 mm away from the glass edge for a soda lime glasssubstrate with a form factor of 65 cm×165 cm. Of course, there can beother variations, alternatives, and modifications. In alternativeembodiments, the trench may have a width of more than or about 90 μm,100 μm, 250 μm, 500 μm, 750 μm, 1 mm, etc. or more. Alternatively, thewidth of the trench may be less than or about 90 μm, 80 μm, 70 μm, 50μm, 25 μm, etc. or less. Additionally, the distance may be less than 4mm, and can be less than or about 3 mm, 2 mm, 1 mm, etc. or less. Instill another alternative, the distance may be more than 4 mm, and maybe more than or about 5 mm, 6 mm, 7 mm, 10 mm, etc. or more.

Referring to FIG. 1 again, the method 100 according to the presentinvention further includes a step 150, for forming one or morethicknesses of precursor materials overlying the patterned conductormaterial. As illustrated in FIG. 6, a first thickness of a firstprecursor material 241 is formed overlying the conductor material 220including filling of the multiple trenches 230. The first precursormaterial also fills in the first trench 231 and covers the conductormaterial 222 beyond the first trench 231 in the peripheral edge regionwith a gradually reduced coverage. In a specific embodiment, the firstthickness of the first precursor material is deposited by sputtering asodium-bearing Cu-Ga target device. The sputter process is performed atnear room temperature with DC magnetron sputtering technique. The targetdevice is well selected to have a predominant (>90% wt %) copper-galliumspecies and mixed with about 8 wt % of Na₂SeO₃ species. The sodiumbearing target device disposed in the compartment includes apredetermined sodium composition and predominant amount (>90 wt %) ofcopper-gallium species. Near room temperature deposition suppresses thediffusion of ionic species within the first precursor material andbetween the film of the first precursor material and the conductormaterial underneath.

In a specific embodiment, the step 150 includes further forming one ormore thicknesses of precursor materials. As illustrated in FIG. 7, asecond thickness of the second precursor material 242 is formedoverlying the first precursor material 241. In an example, the secondprecursor material is deposited by sputtering a second target devicecontaining copper-gallium alloy. The deposition is still performed attemperatures near room temperature. Furthermore, a third thickness ofthe third precursor material 243 is formed overlying the secondprecursor material 242, by sputtering a third target device containingprimarily pure indium species. Of course, the formation of the one ormore precursor materials as described above is part of two-stage processfor forming a thin-film photovoltaic absorber. The first stage is a lowtemperature (or near room temperature) deposition of the precursormaterials containing copper species, indium species, gallium species,and mixed a proper amount of sodium species (originated from the firsttarget device). The second stage, to be described in a next step withmore details, will execute a chemical treatment process to induce athermal reaction of these precursor materials with one or more reactivegases to transform the precursor material into a multi-graincrystallized compound bearing p-type semiconductor characteristics.

Following the formation of the one or more precursor materials in step150, the method 100 of the present invention in a specific embodimentincludes transferring the glass substrate with the precursor materialsformed overlying the conductor material and barrier material into afurnace system. As shown schematically in FIG. 8, the furnace system 300encloses the soda lime glass substrate 200 as well as the formed filmsabove including a barrier material 210, 212, a conductor material 220,222, the patterned trench structure 230, 231, and the one or moreprecursor materials 241, 242, and 243 in a multi-layered structure. Inthe furnace system 300, the method 100 executes a step 160 for thermallytreating the one or more precursor materials in a heated (ramped up fromroom temperature) environment 320 at temperatures ranging from 400° C.and above to about 550° C. The furnace system 300 is filled withreactive gases 310 including a mixture of selenium species and nitrogen(and hydrogen) species in one embodiment for causing a reactiveselenization process to convert the copper, indium, gallium species inthe precursor materials into a copper-indium-selenide (CIS) orcopper-indium-gallium-selenide (CIGS) compound. In another embodiment,the furnace system 300 is configured to pump out the selenium speciesand refill sulfur species (mixed with nitrogen or hydrogen species) forcausing a sulfurization process to form copper-indium-selenium-sulfide(CISS) or copper-indium-gallium-selenium-sulfide (CIGSS) compound. Acertain amount of sodium species existed in the precursor material helpto improve the grain quality of CIS/CIGS/CIGSS compound during thethermal treatment at temperatures above 400° C. At the end of the step,the furnace system 300 is cooled down to near room temperature again(with a cooling rate as fast as allowed by the system design and glasstransition characteristics), the multi-grain CIS/CIGS/CIGSS compoundbecomes a film of photovoltaic absorber material 240 (FIG. 9),characterized by its electro-optical properties for converting solarlight energy to electrical energy.

As the step 160 is executed as part of the method 100 for manufacturinga thin-film photovoltaic device on the glass substrate, the same step160 also induces some side effects especially due to the elevatedtemperatures and highly reactive chemical environment. Some side effectsinclude sodium species diffusing out of the soda lime glass substrate atthe elevated temperatures through one or more pathways. In anembodiment, the soda lime glass substrate 200 has a rounded androughened edge region 202 that leads to incomplete coverage of barriermaterial 212 in the edge region 202. The sodium species in the soda limeglass substrate are substantially blocked by the barrier materialoverlying the surface region 201 but may pass through some thinnedbarrier material 212 or even bared glass portion in the edge region 202into the conductor material 222. In other words, as shown in FIG. 8, theedge region 202 with thinned barrier material 212 or non-covered portionprovides an easy pathway 301 for the sodium species to diffuse from theglass substrate to an interface region 303 (FIG. 9). Further the sodiumspecies may build up excessively near the interface region 303 betweenthe conductor material 222 and the film of the photovoltaic absorber 240and may continue to expand the build up towards the conductor material220 on the nearby surface region 201. As noted above, excessive sodiumspecies buildup in the interface region may weaken the adhesion of thefilm on the conductor material 220 and causes the film peeled off whensubjecting to large temperature variation. The film peeling starts fromthe films near the edge region 202 resulting from the excessive sodiumspecies in region 303, and may extend to larger area in the nearbysurface region 201. After the thermal treatment process conducted aboveand additional high temperature vapor deposition process followed thetreatment process for forming an upper electrical contact material 250(as seen in FIG. 10) over the film of the photovoltaic absorber 240,film peeling problem may occur.

In the worst scenario, the film peeling may occur at the inner surfaceregion so that any edge deletion afterward cannot eliminate the problemwhich causes the module failure. In a specific embodiment of the presentinvention, the first trench 231 as formed in the step 140 creates aphysical barrier for those sodium species through the above pathway inthe edge region. It is found that the sodium species diffuse, at theelevated temperatures, with much higher rate in molybdenum material thanin copper-gallium alloy material. After the molybdenum material isremoved in the step 140 out of the first trench, the first trench isrefilled by the copper-gallium alloy in the step 150 (the firstprecursor material 241), the sodium diffusion is substantiallysuppressed during the step 160. Therefore, the first trench 231effective restricts the sodium buildup problem only to the peripheraledge region and prevents the film of the photovoltaic absorber material240 in the surface region from peeling off the conductor material 220.This is achieved without any other costly edge treatment of the glasssubstrate before start the manufacture of thin-film photovoltaic deviceson the glass substrate according to embodiments of the presentinvention.

Referring to FIG. 1, the method 100 stops at the step 190, In analternative embodiment, the first trench 231 continues to serve as aphysical barrier for blocking the open sodium diffusion path during oneor more additional processes following the thermal treatment step 160.One process, for example, includes a wet process using chemical bathdeposition technique to deposit a thin layer (about 10 nm) ofaluminum-zinc-oxide (AZO) and/or a buffer layer of cadmium sulfide. Theimmersion of the soda lime glass substrate (plus all films formedthereon) in an aqueous solution (for the wet process) causes theadhesion failure of the photovoltaic absorber material from theconductor material (Mo), possibly by dissolving a sodium rich interfaceregion. Additionally, as shown in FIG. 10, an upper transparentconductive material 250 is formed overlying (the thin AZO layer and) thephotovoltaic absorber material 240. In an embodiment, the uppertransparent conductive material 250 is a transparent conductive oxidematerial made by a chemical vapor deposition, which also is conducted atrelative high temperature and chemically reactive environment. Forexample, the transparent conductive oxide (TCO) material often uses zincoxide (ZnO). The TCO material of about 2 μm in thickness over theabsorber material may cause extra interface stress that further inducesfilm peeling effect at the interface between the absorber and conductorwhere the adhesion failure occurs due to the existence of sodium speciesleaked from the glass substrate. In certain embodiments, as sodiumspecies builds up in the edge region 303 between the film of thephotovoltaic absorber material 240 and the conductive material (Mo) 222in the edge region, the chemically active agent in gas phase environmentmay cause reaction with the active Na⁺ ions there. This will furtherweaken the atomic bonding in local film structure and weakens the filmadhesion. Therefore, having the first trench 231 formed as a protectionbarrier surrounding the surface region, any above film structure damagesin the peripheral edge region can be disregarded and the film of thephotovoltaic absorber material 240 formed in the surface region issubstantially free from any peel-off problem.

FIG. 11 shows additional steps performed after the upper conductivematerial formation (FIG. 10) towards a completion of the manufacture ofthin-film photovoltaic devices on the substrate. In particular, theadditional steps include another patterning process to form the upperelectrode structure for a plurality of thin-film photovoltaic cellswithin the surface region (under the protection of the first trench231). The present patterning process causes a formation of multipletrenches 430 (and filled with conductor or insulator material) which arecorrelated to multiple line trenches 230 formed during the patterningprocess in step 140. The combination of these correlated pattern 430 and230 results in a formation of a plurality of cells 400 mutually coupledelectrically. In another embodiment, the additional steps include anedge deletion process after the formation of all the cell structures 400to remove most film materials except the lower conductor material in anenlarged edge region including the area around the first trench 231. Asseen in FIG. 11, this process creates a region for forming electricalcoupling band between cells and external electrode leads. In a specificembodiment, the enlarged edge region has a width up to 15 mm measuredfrom the glass edge. The same process also eliminates the peeled filmmaterial within the peripheral edge region. However, the edge deletionprocess cannot completely eliminate the film peeling problem as thedamages created in earlier processes may have extended to surface regiongreater than the edge deletion width, e.g., the 15 mm. Of course, thereare many variations, alternatives, and modifications.

FIG. 12 is a simplified diagram showing a top view of a thin film withstripe patterned structure on a substrate with and a trench formed in avicinity of peripheral edge region according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims herein. One of ordinary skill inthe art would recognize many variations, alternatives, andmodifications. In this top view, a whole area of a thin-filmphotovoltaic module formed on a rectangular shaped glass substrate witha form factor of 65 cm×165 cm is presented. Each stripe region 400 seenin FIG. 12 represents one of the plurality of photovoltaic cellsseparated by a line pattern 430 formed after the patterning processdescribed in FIG. 11. The first trench 231 is also seen located aroundthe peripheral edge region.

FIG. 13 is a simplified diagram showing a top view of a thin film withstripe patterned structure on a substrate with edge-region film materialdeleted according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims herein. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The thin-film photovoltaicmodule shown in FIG. 12 is subjected to an edge deletion process asdescribed in FIG. 11. In this top view, an edge region 410 with anenlarged width (including the first trench 231 and beyond) is carried alaser ablation treatment or a mechanical scrap process to remove mostabsorber material and upper conductive material. For the glass substratewith a form factor of 65 cm×165 cm, the enlarged width can be up to 15mm. This region will be further processed to incorporate cell's electriccontact and external leads. Further in a specific embodiment, the modulewill be laminated with a top glass panel with mask tape being applied onthe electrical contact and the edge region being sealed with anedge-seal material, followed by assembling with a frame structure.

It is also understood that the examples, figures, and embodimentsdescribed herein are for illustrative purposes only and that variousmodifications or changes in light thereof will be suggested to personsskilled in the art and are to be included within the spirit and purviewof this application and scope of the appended claims. Further details ofthe method for manufacturing a thin-film solar module substantially freeof any film peeling can be found throughout the present specification.

What is claimed is:
 1. A film structure for manufacturing a photovoltaicdevice free of peeling effect, the structure comprising: a glasssubstrate having a surface region and a bulk region, the bulk regioncomprising sodium species, the surface region being surrounded by aperipheral edge region; a barrier material overlying the surface regionand partially overlying the peripheral edge region; a conductor materialoverlying the barrier material and partially overlying the peripheraledge region; a first trench with the substantially all the conductormaterial therein being removed, the first trench being at least formed aclosed loop in a vicinity of the peripheral edge region surrounding thesurface region; one or more thicknesses of precursor materials overlyingthe conductor material and at least partially filling the first trench,wherein the one or more thicknesses of precursor materials beingsubjected to an environment of reactive Selenium gaseous species attemperatures above 400° C. and transformed into a film of photovoltaicabsorber, and the film of photovoltaic absorber is characterized bysubstantially free from peeling-off the conductor material anywherewithin the surface region surrounded by the first trench.
 2. The filmstructure of claim 1 wherein the glass substrate comprises a soda limeglass panel.
 3. The film structure of claim 1 wherein the barriermaterial comprises a film material selected from silicon oxide, orsilicon nitride, or silicon oxynitride, or aluminum-containing siliconoxide.
 4. The film structure of claim 1 wherein the first trench islocated about 4 mm or smaller away from the peripheral edge region ofthe glass substrate.
 5. The film structure of claim 1 wherein the firsttrench comprises a width of about 90 μm and greater and a depth at leastequal to a thickness of the conductor material.
 6. The film structure ofclaim 1 wherein the first trench comprises a physical barrier tosubstantially block all sodium species diffusing from the peripheraledge region into the conductor material to induce film peeling in theinterface between the conductor material and the film of photovoltaicabsorber.
 7. The film structure of claim 1 wherein the one or morethicknesses of precursor materials comprises a first thickness ofsodium-bearing copper-gallium species, a second thickness ofcopper-gallium species, and a third thickness of indium species.